In the field of forest management, a major problem continually being faced is that of quickly establishing a new and healthy crop of trees after the old crop has been harvested. Three methods of establishing a new crop of trees are currently in use: (1) transplanting small trees from nursery beds, (2) natural seeding from nearby mature trees, and (3) scattering seed by hand or from aircraft. The present invention is primarily concerned with the first method.
A common way to transplant young forest trees from nursery beds is to set them into the soil without application of any fertilizers or chemicals. As the trees mature, tree mortality due to disease is often high, and the growth potential of the trees can be significantly reduced due to lack of nutrients.
By way of example, one disease that causes particular damage among intensively managed pine forests in the southern United States is fusiform rust disease. This disease is caused by the fungus Cronartium ouercuum f. sp. fusiforme. Spores of this fungus are carried through the air during a "spore-flight season." Upon being infected by the fungus, the tree develops the characteristic fusiform (elliptical or oval) "galls" for which the disease is named. The disease interferes with the growth and development of the trees, particularly the slash and loblolly varieties of pine trees. Unchecked spread of the disease causes a marked reduction in the height and diameter of the trees, thereby resulting in a net decrease in the amount of usable timber which can be harvested per acre of land. Severely infected trees also tend to develop an excessive number of branches or stems, giving them a "bush-like" appearance and reducing their value as a source of timber. In short, the disease is a major obstacle to the proper growth of forest trees.
While the maturing trees are still in nursery beds, it is possible to control the incidence of the disease by repeatedly spraying the trees with a systemic fungicide (such as the fungicide Bayleton.RTM.) at one month intervals during the spore-flight season. However, once the trees are transplanted into forests, it is exceedingly expensive, and therefore impractical, to continue spraying the trees with fungicides. As a result, it is common practice simply to transplant the trees without any further application of chemicals to control the disease. Since the immature trees are particularly susceptible to disease after they are transplanted, they provide a vulnerable target for the fusiform rust fungus. As a result, in some areas the incidence of the disease in slash pines can reach 50% or higher.
Trees that are uninfected by fusiform rust disease by age 5 are likely to grow to maturity for commercial harvest. Accordingly, a need exists for a slow-release pesticide in which the pesticide control agent is designed to have an extended release period so that the seedlings can mature to age 5 without significant infection by the fungus.
It is known to provide slow-release fertilizer material by mixing nitrogen, phosphorus, potassium, and micronutrient sources with inert binding materials or urea formaldehyde resins to retard the generally rapid rate of leaching of fertilizer salts. For example, U.S. Pat. No. 3,925,053 discloses a slow acting fertilizer composition in which a hemihydrate of calcium sulfate is used as a binder to bond the fertilizer materials.
Such bonded fertilizer compositions may also be manufactured in the form of a spike or a briquette. For example, U.S. Pat. No. 3,647,416 discloses a slow-release fertilizer spike comprising a water-soluble urea-formaldehyde resin, a granular filler material, and a binder derived from magnesia and phosphoric acid. The extruded spikes have a high crushing strength. Likewise, U.S. Pat. No. 3,024,098 discloses a fertilizer product produced by preparing a finely divided mass comprising essentially at least one nutrient constituent selected from the group consisting of certain urea-formaldehyde compounds and phosphorus-containing compounds. The mass is then compressed into unitary products of substantially uniform size. The resulting product contains nutrient in a highly concentrated but slowly soluble form which may be placed at the bottom of a planting hole at the time a seedling is transplanted.
Although these products have a high crushing strength, they typically contain some water soluble ingredients which cause them to lose their integrity relatively rapidly when immersed in water. Excessive moisture generated during hard rains may cause accelerated and wasteful consumption and leaching of the fertilizer materials. Soaking rains can cause concentration of plant food salts in the vicinity of the plant roots which may damage the plant.
Greater success is had when relatively insoluble fertilizer materials are formed into briquettes. For example, U.S. Pat. No. 4,304,589 discloses a briquetted fertilizer for forest fertilization which comprises compression molded granular isobutylidene diurea (which is relatively insoluble in water) and heavy mineral oil. The fertilizer is capable of maintaining its fertilizing effect for from 3 to 5 years.
Prior efforts to control the release of pesticides in the soil have centered primarily around methods of encapsulation, dissolution, or incorporation of the active ingredient. Release rate of the pesticide is governed by the coating permeability, dissolution rate of the active ingredient, or the permeability of the carrier (elastomers, polyvinyl chloride, or hydrophobic binders). For example, U.S. Pat. No. 3,062,637 discloses a granular aggregate of an active agricultural ingredient (such as plant nutrients, herbicides, algicides, and/or insecticidal toxicants), a particulate nocolloidal mineral carrier, and a colloidal clay as the binder for the aggregate. These efforts have generally met with limited success, due to uneven or uncontrollable release patterns of the pesticide. In addition, the release rate is often too rapid for the effective long-term control of diseases such as fusiform rust.
Accordingly, it is an object of the present invention to provide a fertilizer/pesticide composition which dissolves gradually in the soil to slowly provide the active ingredient of a desirable pesticide, thereby obviating the need for repeated applications of pesticide to maturing plants.
It is a further object of the present invention to provide a fertilizer/pesticide composition which provides long-term fertilization in addition to pesticide protection, thereby saving labor and enhancing the Potential for plant growth and health.
It is yet a further object of the present invention to provide a fertilizer/pesticide composition which is not toxic to the plant when placed adjacent to the root system and which is, therefore, safe for maturing plants.
It is yet a further object of the present invention to provide a fertilizer/pesticide composition which is simple to apply and safe to workers and the environment.
If is yet a further object of the present invention to provide a fertilizer/pesticide composition which is cost-effective and which may be made by readily available manufacturing methods.